The present invention relates to an a-selenium-tellurium photosensitive member having spectral sensitivity in visible light region, particularly in long wavelength region, and having low dark potential, and it also relates to an electrostatic information recording method using such photosensitive member.
Conventionally, silver salt photographing method is known as a photographing technique with high sensitivity. In this photographing technique, the photographed image is recorded on film and the like through development process. To reproduce the image, silver salt emulsion (such as photographic paper) is used or the developed film is optically scanned and the image is reproduced on cathode ray tube (CRT).
Also, an electrophotographic technique is known. In this technique, an electrode is vacuum-deposited on photoconductive layer, and electric charging over the whole surface of the photoconductive layer is performed by corona charging in dark place. Then, it is exposed to strong light to turn the exposed portion of the photo-conductive layer to conductive. By leaking and removing the electric charge on that portion, electrostatic latent image is optically formed on the surface of the photoconductive layer. By attaching toner having electric charge with the polarity opposite to the residual electrostatic charge (or electric charge with the same polarity), the image is developed. This technique is mostly used for duplicating purpose. Because of low sensitivity, it cannot be used for photographing, and toner development is usually performed immediately after electrostatic latent image is formed because electrostatic charge retaining time is short.
In the television photographing technique, the image is photographed by pickup tube, and the image information obtained through photoconductor is taken up as electric signal, and this is outputted directly on CRT or recorded on video by magnetic recording, and it is then outputted on CRT at the desired time.
Silver salt photographing method is advantageous in preserving the photographed image, while development process is required to form silver salt image. In reproducing the image, complicated optical, electrical or chemical processings are required to obtain hard copy, soft copy (CRT output), etc.
The electrophotographing technique is advantageous in that it is simpler and faster than silver salt photographing method in reproducing electrostatic latent image, while it is inferior to silver salt method in the point that the time of latent image preservation is extremely short and it is inferior in the dissociation of developer and image quality.
In the television photographing technique, electric signal obtained by pickup tube is taken out, and linear sequential scanning is required for recording. Linear sequential scanning is performed by electron beam in pickup tube or by magnetic head in video recording. Because the resolution depends upon the number of scanning lines, it is extremely inferior to planar analog recording such as silver salt photographing.
The same applies to the resolution in case of television photographing system using solid-state image pickup element (such as CCD) developed in recent year.
The problems with these techniques are such that the processing is complicated when image can be recorded in high quality and high resolution, while memory function is missing or image quality is basically inferior when the process is simpler.
In an electrostatic information recording method, a photosensitive member comprising a photoconductive layer provided with an electrode on front thereof and an electric charge carrying medium comprising an electric charge retaining layer provided with an electrode on backside thereof are placed face-to-face along optical axis, and electrostatic latent image corresponding to the incident light image is formed on the electric charge carrying medium by the exposure to light under voltage application between two electrodes. When amorphous selenium layer (a-Se layer) is used as photoconductive layer in the photosensitive member, a problem arises that the sensitivity to red color is low.
a-selenium is known as a substance to generate positive electric charge under light irradiation and also as a substance to transport positive electric charge (hole). Because of the band gap of about 2.0 eV, it has almost no sensitivity to visible light having wavelength of 600-700 nm although it has sufficient sensitivity to the light having wavelength of 500 nm or less. Therefore, by doping tellurium to selenium, it is attempted to reduce the band gap and to provide high sensitivity to the light of long wavelength.
However, because tellurium itself has no photoconductive property, thermal excitation carrier increases when tellurium quantity is increased, and the increase of dark current is induced. Specifically, selenium and electrode form a so-called blocking contact and prevents the electric charge injected from the electrode. When tellurium is added, the blocking property is weakened.
On the other hand, it is necessary to have electric charge generating layer having thickness of 5-3 .mu.m in order to increase the availability of light. However, to prevent the electric charge injected from the electrode with such thickness, the quantity of tellurium can only be increased by 20-25 wt % at the highest. Even when the electric charge preventive layer of about 0.1 .mu.m thick is provided to prevent the injection of electric charge, the electric charge is increased when the quantity of tellurium exceeds 30 wt %, and spectral sensitivity cannot be obtained in the long wavelength region.
To solve the above problems, the object of the present invention is to offer an electrostatic information recording method, by which it is possible to perform recording for long time with high quality and high resolution with simpler process by the use of a-selenium-tellurium photosensitive member, which has spectral sensitivity for long wavelength region and having low dark potential. It is also possible to repeatedly reproduce the memorized characters, diagrams, images, codes, or (1.0) information for each purpose and with the desired image quality at the desired time.